[llvm] [LAA] Be more careful when evaluating AddRecs at symbolic max BTC. (PR #128061)

[Ramkumar Ramachandra via llvm-commits]

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@@ -206,11 +206,31 @@ std::pair<const SCEV *, const SCEV *> llvm::getStartAndEndForAccess(
   const SCEV *ScStart;
   const SCEV *ScEnd;
 
+  auto &DL = Lp->getHeader()->getDataLayout();
+  Type *IdxTy = DL.getIndexType(PtrExpr->getType());
+  const SCEV *EltSizeSCEV = SE->getStoreSizeOfExpr(IdxTy, AccessTy);
   if (SE->isLoopInvariant(PtrExpr, Lp)) {
     ScStart = ScEnd = PtrExpr;
   } else if (auto *AR = dyn_cast<SCEVAddRecExpr>(PtrExpr)) {
     ScStart = AR->getStart();
-    ScEnd = AR->evaluateAtIteration(MaxBECount, *SE);
+    if (!isa<SCEVCouldNotCompute>(BTC))
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artagnon wrote:

Not sure why we are passing the exact BTC, and handling the case where it is a could-not-compute. Why not just pass the symbolic max as before, and have the logic below?

https://github.com/llvm/llvm-project/pull/128061